PSI - Issue 54

Robin Depraetere et al. / Procedia Structural Integrity 54 (2024) 172–179 R. Depraetere et al. / Structural Integrity Procedia 00 (2023) 000–000

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Fig. 2: Normalized force versus true strain curves of the uncharged ( C L , 0 = 0 wppm) and hydrogen charged ( C L , 0 = 0 . 33 wppm) specimens. The specimens that are not scanned using X-ray micro-CT are shown more transparent.

(a)

(b)

Fig. 3: (a) Average fracture strain for each specimen geometry, comparing the uncharged ( C L , 0 = 0 wppm) and hydrogen charged ( C L , 0 = 0 . 33 wppm) specimens. The number of tests per geometry and condition n is displayed in the figure. The error bars represent the range between the minimum and maximum values. (b) Illustrative fracture surfaces for specimen geometry R2, obtained with SEM.

The shape of each individual void was characterized through its aspect ratios ∆ L / ∆ S and ∆ T / ∆ S , where ∆ L , ∆ S and ∆ T represent the dimensions of the bounding box of the void in the L (longitudinal-to-rolling), S (through thickness) and T (transverse-to-rolling) direction, respectively.

3. Results

3.1. Macroscopic measurements

The normalized force F / A 0 versus the true strain ϵ t is displayed in Figure 2 for each tested specimen. The presence of hydrogen in the steel results in a small average loss in ductility. This is more apparent when visualizing the fracture strains ϵ f in Figure 3a. Average reductions in ϵ f ranging from 4% (for R1.2) till 25% (for R2) are observed. There is no clear trend regarding the influence of the stress triaxiality on the reduction in ϵ f . Scanning electron microscopy (SEM) was used to investigate the fracture surfaces. Figure 3b displays illustra tive fracture surfaces for specimen geometry R2. The fracture surfaces of both the uncharged and hydrogen charged specimens predominantly consist of ductile dimples, clearly elongated in the T direction. A limited amount of quasi cleavage was observed for the hydrogen charged specimens.